Methods and apparatus for estimation of ventricular afterload based on ventricular pressure measurements

1. A method of deriving an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

determining the peak positive pressure value P b , the peak positive derivative pressure dP/dt PP and the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

determining the sample time t b of peak positive pressure, the sample time t a of the peak positive derivative pressure dP/dt PP , and the sample times t c of the peak negative derivative pressure dP/dt NP from the sample times associated with the set of ventricular pressure values; and

calculating an index α of the relative timing of peak positive pressure P b in the blood ejection phase in accordance with the formula α=(t b −t a )/(t c−t a ), wherein the severity of ventricular afterload is proportional to the value of index α in the range between 0 and 1.

2. The method of claim 1 , further comprising:

determining the decreasing pressure P c associated with the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values; and

calculating an index β of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β=(P c −P b )/(t c −t b ), wherein the severity of ventricular afterload is proportional to the magnitude of the index β.

3. The method of claim 2 , wherein the obtaining step further comprises obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

4. The method of claim 2 , wherein the obtaining step further comprises obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

5. A method of deriving an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

determining the peak positive pressure value P b , the peak negative derivative pressure dP/dt NP , and the decreasing pressure P c associated with the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

determining the sample time t b of peak positive pressure, and the sample time t c of the peak negative derivative pressure dP/dt NP from the sample times associated with the set of ventricular pressure values; and

calculating an index β of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β=(P c −P b )/(t c −t b ), wherein the severity of ventricular afterload is proportional to the magnitude of the index β.

6. The method of claim 5 , wherein the obtaining step further comprises obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

7. The method of claim 5 , wherein the obtaining step further comprises obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

8. In an implantable heart monitor adapted to be implanted in a patient's body and comprising a pressure sensor coupled with pressure signal processing circuitry and memory for data storage, a method of deriving an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

operating the pressure sensor to obtain a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

determining the peak positive pressure value P b , the peak positive derivative pressure dP/dt PP and the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

determining the sample time t b of peak positive pressure, the sample time t a of the peak positive derivative pressure dP/dt PP , and the sample time t c of the peak negative derivative pressure dP/dt NP from the sample times associated with the set of ventricular pressure values;

calculating an index α of the relative timing of peak positive pressure P b in the blood ejection phase in accordance with the formula α=(t b −t a )/(t c −t a ), wherein the severity of ventricular afterload is proportional to the value of index α in the range between 0 and 1; and

storing the calculated index α in data storage memory.

9. The method of claim 8 , further comprising:

determining the decreasing pressure P c associated with the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

calculating an index β of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β=(P c −P b )/(t c −t b ), wherein the severity of ventricular afterload is proportional to the magnitude of the index β; and

storing the calculated index β in data storage memory.

10. The method of claim 8 , wherein the obtaining step further comprises obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

11. The method of claim 8 , wherein the obtaining step further comprises obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

12. In an implantable heart monitor adapted to be implanted in a patient's body and comprising a pressure sensor coupled with pressure signal processing circuitry and memory for data storage, a method of deriving an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

determining the peak positive pressure value P b , the peak negative derivative pressure dP/dt NP , and the decreasing pressure P c associated with the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

determining the sample time t b of peak positive pressure, and the sample time t c of the peak negative derivative pressure dP/dt NP from the sample times associated with the set of ventricular pressure values; and

calculating an index β of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β=(P c −P b )/(t c −t b ), wherein the severity of ventricular afterload is proportional to the magnitude of the index β; and storing the calculated index β in data storage memory.

13. The method of claim 12 , wherein the obtaining step further comprises obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

14. The method of claim 12 , wherein the obtaining step further comprises obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

15. The method of claim 12 , wherein the implantable medical device adapted to be implanted in the patient's body comprises means for delivering a therapy in accordance with adjustable therapy delivery operating modes and parameters.

16. In an implantable medical device adapted to be implanted in a patient's body for delivering a therapy in accordance with adjustable therapy delivery operating modes and parameters comprising a pressure sensor coupled with pressure signal processing circuitry and therapy delivery means for delivering a therapy, a method of deriving an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

determining the peak positive pressure value P b , the peak positive derivative pressure dP/dt PP and the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

determining the sample time t b of peak positive pressure, the sample time t a of the peak positive derivative pressure dP/dt PP , and the sample time t c of the peak negative derivative pressure dP/dt NP from the sample times associated with the set of ventricular pressure values;

calculating an index α of the relative timing of peak positive pressure P b in the blood ejection phase in accordance with the formula α=(t b −t a )/(t c −t a ), wherein the severity of ventricular afterload is proportional to the value of index α in the range between 0 and 1; and

adjusting one of a therapy delivery operating mode or parameter to minimize the value of index α.

17. The method of claim 16 , further comprising:

determining the decreasing pressure P c associated with the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

calculating an index β of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β=(P c −P b )/(t c −t b ), wherein the severity of ventricular afterload is proportional to the magnitude of the index β; and

adjusting one of a therapy delivery operating mode or parameter to minimize the magnitude of index β.

18. The method of claim 16 , wherein the obtaining step further comprises obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

19. The method of claim 16 , wherein the obtaining step further comprises obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

20. In an implantable medical device adapted to be implanted in a patient's body for delivering a therapy in accordance with adjustable therapy delivery operating modes and parameters comprising a pressure sensor coupled with pressure signal processing circuitry and therapy delivery means for delivering a therapy, a method of deriving an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

determining the peak positive pressure value P b , the peak negative derivative pressure dP/dt NP , and the decreasing pressure P c associated with the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

determining the sample time t b of peak positive pressure, and the sample time t c of the peak negative derivative pressure dP/dt NP from the sample times associated with the set of ventricular pressure values; and

calculating an index β of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β=(P c −P b )/(t c −t b ), wherein the severity of ventricular afterload is proportional to the magnitude of the index β; and

adjusting one of a therapy delivery operating mode or parameter to minimize the magnitude of index β.

21. The method of claim 20 , wherein the obtaining step further comprises obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

22. The method of claim 20 , wherein the obtaining step further comprises obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

23. Apparatus that derives an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

means for obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

means for determining the peak positive pressure value P b , the peak positive derivative pressure dP/dt PP and the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

means for determining the sample time t b of peak positive pressure, the sample time t a of the peak positive derivative pressure dP/dt PP , and the sample time t c of the peak negative derivative pressure dP/dt NP from the sample times associated with the set of ventricular pressure values; and

means for calculating an index α of the relative timing of peak positive pressure P b in the blood ejection phase in accordance with the formula α=(t b −t a )/(t c −t a ), wherein the severity of ventricular afterload is proportional to the value of index α in the range between 0 and 1.

24. The apparatus of claim 23 , further comprising:

means for determining the decreasing pressure P c associated with the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values; and

means for calculating an index β of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β=(P c −P b )/(t c −t b ), wherein the severity of ventricular afterload is proportional to the magnitude of the index β.

25. The apparatus of claim 23 , wherein the obtaining means further comprises means for obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

26. The apparatus of claim 23 , wherein the obtaining means further comprises means for obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

27. Apparatus that derives an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

means for obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

means for determining the peak positive pressure value P b , the peak negative derivative pressure dP/dt NP , and the decreasing pressure P c associated with the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

means for determining the sample time t b of peak positive pressure, and the sample time t c of the peak negative derivative pressure dP/dt NP from the sample times associated with the set of ventricular pressure values; and

means for calculating an index β of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β=(P c −P b )/(t c −t b ), wherein the severity of ventricular afterload is proportional to the magnitude of the index β.

28. The apparatus of claim 27 , wherein the obtaining means further comprises means for obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

29. The apparatus of claim 27 , wherein the obtaining means further comprises means for obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

30. In an implantable heart monitor adapted to be implanted in a patient's body and comprising a pressure sensor coupled with pressure signal processing circuitry and memory for data storage, apparatus that derives an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

means for operating the pressure sensor to obtain a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

means for determining the peak positive pressure value P b , the peak positive derivative pressure dP/dt PP and the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

means for determining the sample time t b of peak positive pressure, the sample time t a of the peak positive derivative pressure dP/dt PP , and the sample time t c of the peak negative derivative pressure dP/dt NP from the sample times associated with the set of ventricular pressure values;

means for calculating an index α of the relative timing of peak positive pressure P b in the blood ejection phase in accordance with the formula α=(t b −t a )/(t c −t a ), wherein the severity of ventricular afterload is proportional to the value of index α in the range between 0 and 1; and

means for storing the calculated index α in data storage memory.

31. The apparatus of claim 30 , further comprising:

means for determining the decreasing pressure P c associated with the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

means for calculating an index β of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β=(P c −P b )/(t c −t b ), wherein the severity of ventricular afterload is proportioned to the magnitude of the index β; and

means for storing the calculated index β in data storage memory.

32. The apparatus of claim 30 , wherein the obtaining means further comprises means for obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

33. The apparatus of claim 30 , wherein the obtaining means further comprises means for obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

34. In an implantable heart monitor adapted to be implanted in a patient's body and comprising a pressure sensor coupled with pressure signal processing circuitry and memory for data storage, apparatus that derives an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

means for obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

means for determining the peak positive pressure value P b , the peak negative derivative pressure dP/dt NP , and the decreasing pressure P c associated with the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

means for determining the sample time t b of peak positive pressure, and the sample time t c of the peak negative derivative pressure dP/dt NP from the sample times associated with the set of ventricular pressure values;

means for calculating an index β of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β=(P c −P b )/(t c −t b ), wherein the severity of ventricular afterload is proportional to the magnitude of the index β; and

means for storing the calculated index β in data storage memory.

35. The apparatus of claim 34 , wherein the obtaining means further comprises means for obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

36. The apparatus of claim 34 , wherein the obtaining means further comprises means for obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

37. In an implantable medical device adapted to be implanted in a patient's body for delivering a therapy in accordance with adjustable therapy delivery operating modes and parameters comprising a pressure sensor coupled with pressure signal processing circuitry and therapy delivery means for delivering a therapy, apparatus that derives an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

means for obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

means for determining the peak positive pressure value P b , the peak positive derivative pressure dP/dt PP and the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

means for determining the sample time t b of peak positive pressure, the sample time t a of the peak positive derivative pressure dP/dt PP , and the sample time t c of the peak negative derivative pressure dP/dt NP from the sample times associated with the set of ventricular pressure values;

means for calculating an index α of the relative timing of peak positive pressure P b in the blood ejection phase in accordance with the formula α=(t b −t a )/(t c −t a ), wherein the severity of ventricular afterload is proportional to the value of index α in the range between 0 and 1; and

means for adjusting one of a therapy delivery operating mode or parameter to minimize the value of index β.

38. The apparatus of claim 37 , further comprising:

means for determining the decreasing pressure P c associated with the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

means for calculating an index β of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β=(P c −P b )/(t c −t b ), wherein the severity of ventricular afterload is proportional to the magnitude of the index β; and

means for adjusting one of a therapy delivery operating mode or parameter to minimize the magnitude of index β.

39. The apparatus of claim 37 wherein the obtaining means further comprises means for obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

40. The apparatus of claim 37 , wherein the obtaining means further comprises means for obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.

41. In an implantable medical device adapted to be implanted in a patient's body for delivering a therapy in accordance with adjustable therapy delivery operating modes and parameters comprising a pressure sensor coupled with pressure signal processing circuitry and therapy delivery means for delivering a therapy, apparatus that derives an index of ventricular afterload presenting resistance to ejection of blood from a ventricle during a blood ejection phase comprising:

means for obtaining a set of ventricular pressure values of blood pressure within a ventricle at sample times during the blood ejection phase of the ventricle;

means for determining the peak positive pressure value P b , the peak negative derivative pressure dP/dt NP , and the decreasing pressure P c associated with the peak negative derivative pressure dP/dt NP from the set of ventricular pressure values;

means for determining the sample time t b of peak positive pressure, and the sample time t c of the peak negative derivative pressure dP/dt NP from the sample times associated with the set of ventricular pressure values;

means for calculating an index β of the slope of the early ejection pressure in the blood ejection phase in accordance with the formula β=(P c −P b )/(t c −t b ), wherein the severity of ventricular afterload is proportional to the magnitude of the index β; and

means for adjusting one of a therapy delivery operating mode or parameter to minimize the magnitude of index β.

42. The apparatus of claim 41 , wherein the obtaining means further comprises means for obtaining a set of right ventricular pressure values of right ventricular blood pressure within a right ventricle at sample times during the blood ejection phase of the right ventricle.

43. The apparatus of claim 41 , wherein the obtaining means further comprises means for obtaining a set of left ventricular pressure values of left ventricular blood pressure within a left ventricle at sample times during the blood ejection phase of the left ventricle.